1. Field of the Invention
The present invention relates to a signal processing apparatus and, more specifically, relates to a signal processing apparatus that can carry out appropriate compensation within a predetermined amount of time and prevent degradation of image quality even when the number of pixels in a solid-state image-pickup device is increased by neither increasing the driving frequency nor increasing the circuit area.
2. Description of the Related Art
Recently, for apparatuses for recording digital moving images (for example, single-chip digital video cameras) that use one solid-state image-pickup device or apparatuses for recording digital moving images (for example, triple-chip digital video cameras) that use a plurality of solid-state image-pickup devices, the number of pixels included in the solid-state image-pickup devices of such systems has been increasing.
Even under such increase in the number of pixels, in such moving-image capturing systems, their outputs conform to a television signal standard (for example, National Television System Committee (NTSC), Phase Alternation by Line (PAL), or SEquential Couleur A Memoire (SECAM)) and, thus, must be appropriately processed by compensating for the predetermined field frequency (or frame frequency), the horizontal resolution, and the vertical resolution, within a predetermined amount of time.
When the number of pixels obtained from the solid-state image-pickup device (resolution) is small, in general, such appropriate processing is carried out by a configuration shown in FIG. 1.
FIG. 1 is a block diagram illustrating an example of a signal processing system included in a known digital video camera.
As shown in FIG. 1, a signal-processing system 1 is basically constructed of a lens 11, a solid-state image-pickup device 12, an analog/digital (A/D) converter 13, and a camera-signal processing unit 14. The camera-signal processing unit 14 includes a correction processing unit 21 dependent on pixels (hereinafter, simply referred to as a correction processing unit 21), a correction processing unit 22 independent from pixels (hereinafter, simply referred to as an independent correction processing unit 22), a synchronization processing unit 23, a modulation and YC-conversion processing unit 24, and a resolution conversion processing unit 25.
The correction processing unit 21 dependent on pixels carries out correction for a digital video camera using the solid-state image-pickup device 12 while taking into consideration defective pixels, among the pixels in the correction processing unit 21, that output signals at an abnormal level even when light is not incident thereon. As a result, when the quality of a captured image is degraded, the correction processing unit 21 dependent on pixels checks which pixels of the solid-state image-pickup device 12 are defective, and the defective pixels determined as a result of the checkout are corrected.
The lens 11 focuses light L1 from an object on the solid-state image-pickup device 12 as light L2.
The solid-state image-pickup device 12 is constituted of a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), carries out photoelectric conversion by receiving light L1 (light L2) that is from the object and is incident thereon via the lens 11, and outputs an analog image signal E1 that is an electrical signal corresponding to the amount of received light to the A/C converter 13. On the surface of the solid-state image-pickup device 12, red (R), green (G), and blue (B) on-chip color filters (OCCFs) are provided for each light-receiving element constituting each pixel. Only transmissive color components of the OCCFs among the focused light L2 are photoelectrically converted for each pixel.
The A/D converter 13 converts the analog signal E1 supplied from the solid-state image-pickup device 12 and outputs a digital signal S1 to the camera-signal processing unit 14 (correction processing unit 21).
The correction processing unit 21 of the camera-signal processing unit 14 carries out correction processing dependent on the pixels, such as pixel defect compensation processing (Japanese Unexamined Patent Application Publication No. 5-344426 (hereinafter referred to as Patent Document 1)), channel difference adjustment gain processing (Japanese Unexamined Patent Application Publication No. 2002-252808 (hereinafter referred to as Patent Document 2)), and noise reduction processing for pixel units (Japanese Unexamined Patent Application Publication No. 2005-311455 (hereinafter referred to as Patent Document 3)), on the digital signal S1 and outputs the obtained signal S2 to an independent correction processing unit 22.
Patent Document 1 discloses a technology employed by a video camera that is capable of selectively switching between a field readout mode and a frame readout mode in which, when a mode for detecting defective pixels is selected, the readout mode of the image-pickup device is compulsorily changed to a frame readout mode.
Patent Document 2 discloses an apparatus including a CCD image sensor that reads out, line by line, pixel information corresponding to one screen and outputs the pixel information, read out line by line, by separating the information into two channels, i.e., left and right channels. In this apparatus, the black level of the pixel data read out from the CCD image sensor is detected independently for the left and right channels, and the black level is corrected for each channel.
Patent Document 3 discloses a technology for carrying out secondary differentiation after carrying out smoothing and interpolation between a target pixel on which noise reduction is carried out and a peripheral pixel in the periphery of the target pixel, comparing the result of the secondary differentiation with a threshold value, determining whether or not the peripheral pixel is a pixel that can be used for noise reduction, and carrying out noise reduction with a pixel that is determined to be able to be used for noise reduction.
Returning to FIG. 1, the independent correction processing unit 22 carries out processing, such as digital gain processing for applying a uniform gain to all colors in the plane and white balance gain processing for independently applying a gain to each color in the plane in a uniform manner, on the signal S2 supplied from the correction processing unit 21 and outputs the obtained signal S3 to the synchronization processing unit 23.
The synchronization processing unit 23 generates signals R, G, and B having matching spatial phases for each pixel on the basis of the signal S3, and outputs the generated signals R, G, and B to the modulation and YC-conversion processing unit 24. When the signal-processing system 1 is a single-chip system, the spatial sampling point for the signal S3 differs for each color. Therefore, synchronization processing (processing for matching the spatial phases) dependent on the OCCF positional pattern of the solid-state image-pickup device 12 is carried out at the synchronization processing unit 23.
The modulation and YC-conversion processing unit 24 carries out image-quality improvement processing, 1/γ processing, Y-signal generation processing, C-signal generation processing, and so on on the R, G, and B signals supplied from the synchronization processing unit 23 and outputs the obtained video signals Y1 and C1 to the resolution conversion processing unit 25.
The resolution-conversion processing unit 25 carries out processing to convert the video signal Y1 and C1 supplied from the modulation and YC-conversion processing unit 24 into signals conforming to the output format and outputs the obtained video signals Y2 and C2 to an external unit. At the resolution-conversion processing unit 25, processing including, for example, interlace processing and cutout processing of effective image regions (for example, processing to cut out and output only valid regions, not including a margin provided for blurriness correction processing) is carried out as conversion processing conforming to the output format.
The signals output from the resolution-conversion processing unit 25 are used as a signal for recording a moving image or a signal for displaying an image being captured at a processing unit (not shown) that is provided in the subsequent section.
FIG. 2 is a block diagram illustrating an example of another configuration of the known signal-processing unit 1. Components that are the same as those illustrated in FIG. 1 are indicated by the same reference numbers and descriptions thereof are not repeated.
In the signal-processing unit 1 illustrated in FIG. 2, the processing carried out by the correction processing unit 21 illustrated in FIG. 1 is carried out in parallel by a correction processing unit 21-1 and a correction processing unit 21-2, and the processing carried out by the independent correction processing unit 22 illustrated in FIG. 1 is carried out in parallel by an independent correction processing unit 22-1 and an independent correction processing unit 22-2.
Similarly, the processing carried out by the synchronization processing unit 23 illustrated in FIG. 1 is carried out in parallel by a synchronization processing unit 23-1 and a synchronization processing unit 23-2, and the processing carried out by the modulation and YC-conversion processing unit 24 illustrated in FIG. 1 is carried out in parallel by a modulation and YC-conversion processing unit 24-1 and a modulation and YC-conversion processing unit 24-2.
The A/D converter 13 shown in FIG. 2 converts an analog signal E1 supplied from a solid-state image-pickup device 12 into a digital signal, splits the digital signal obtained after the conversion into a digital signal S1-1 and a digital signal S1-2, and outputs the digital signal S1-1 to the correction processing unit 21-1 and the digital signal S1-2 to the correction processing unit 21-2.
The resolution-conversion processing unit 25 illustrated in FIG. 2 carries out processing to convert the video signal Y1-1 and C1-1 supplied from the modulation and YC-conversion processing unit 24-1 and the video signal Y1-2 and C1-2 supplied from the modulation and YC-conversion processing unit 24-2 into signals conforming to the output format and outputs the obtained video signals Y2 and C2 to an external unit.
In the signal processing system 1 illustrated in FIG. 2, the signal S2-1 that is obtained by carrying out processing at the correction processing unit 21-1 is supplied to the independent correction processing unit 22-1, whereas the signal S2-2 that is obtained by carrying out processing at the correction processing unit 21-2 is supplied to the independent correction processing unit 22-2. A combined signal of the signal S2-1 and the signal S2-2 corresponds to the signal S2 illustrated in FIG. 1.
The signal S3-1 that is obtained by carrying out processing at the independent correction processing unit 22-1 is supplied to the synchronization processing unit 23-1, whereas the signal S3-2 that is obtained by carrying out processing at the independent correction processing unit 22-2 is supplied to the synchronization processing unit 23-2. A combined signal of the signal S3-1 and the signal S3-2 corresponds to the signal S3 illustrated in FIG. 1.
Similarly, the R, G, and B signals that are obtained by carrying out processing at the synchronization processing unit 23-1 are supplied to the modulation and YC-conversion processing unit 24-1, whereas the R, G, and B signals that are obtained by carrying out processing at the synchronization processing unit 23-2 are supplied to the modulation and YC-conversion processing unit 24-2. Combined signals of the R, G, and B signals that are obtained by carrying out processing at the synchronization processing unit 23-1 and the R, G, and B signals that are obtained by carrying out processing at the synchronization processing unit 23-2 correspond to the R, G, and B signals illustrated in FIG. 1.
The video signals Y1-1 and C1-1 that are obtained by carrying out processing at the modulation and YC-conversion processing unit 24-1 are supplied to the resolution-conversion processing unit 25, and the video signals Y1-2 and C1-2 that are obtained by carrying out processing at the modulation and YC-conversion processing unit 24-2 are supplied to the resolution-conversion processing unit 25. Combined video signals of the video signals Y1-1 and C1-1 and the video signals Y1-2 and C1-2 correspond to the video signals Y1 and C1 illustrated in FIG. 1.
In this way, by carrying out processing that is carried out at one configuration at a plurality of configurations in parallel, an increase in the driving frequency that is a reference of the operation of the camera-signal processing unit 14 can be prevented.
As shown in FIGS. 1 and 2, in the known signal processing system 1, conversion processing conforming to the output format is carried out as the last step in the process.